# Basic Two Dimensional Array Examples

```public class TwoDim {

public static void main(String [] args) {
double scores[][] = new double; //Number of rows & columns, counting from 1
scores  = 95;
scores  = 88;
scores  = 86;
scores  = 90;
scores  = 78;
scores  = 55;

for(int row=0; row < scores.length; row++) { //Starting from first row, all the way to last row
for(int col=0; col<scores[row].length; col++) { //Starting from first column, all the way to last column
System.out.print(scores[row][col] + "\t"); //Print the value in the specified cell
}
System.out.println(); //next line
}
}
}```
```public class TwoDimensionalArray {
public static void main(String [] args) {
double[][] scores = {{95, 88, 86},{90,78,55}}; //{column1{row 1 elements}column2{row 2 elements}}
for(int row=0; row < scores.length; row++) { // Start at row 0, to max row, add 1 to row variable to satisfy Loop & to move to next column
for(int column=0; column < scores[row].length; column++) { //Start at column 0, to max column, add 1 to column variable to satisfy Loop & to move to next column
System.out.print(scores [row] [column] + " ");
}
System.out.println();
}
}
}``` ```/**
* 1. (Sum elements column by column)Write a method that returns the sum of all the elemnts in a specified column in a matrix using the following header:
*     public static double sumColumn(double[][] m, int columnIndex)
* 2. Write a test program that reads a 3-by-4 matrix and displays the sum of each column.
*
* Algorithm:
* Write a test program that reads a 3 by 4 matrix and displays the sum of each column.
* > Make a 3 by 4 matrix
* > Assign values to the 3-by-4 matrix
* > reads a 3 by 4 matrix
* > displays the sum of each column
*/

import java.util.Scanner;

public class ColumnSumArray {
public static void main(String [] args){
//First things first. Let's make a 3 by 4 matrix.
double[][] matrix = new double;

//Which specific column do you want the sum for?
Scanner input = new Scanner(System.in);
System.out.println("Which column Sum do you want? 1, 2, 3, or 4?");
int columnIndex = input.nextInt();

double reType = sumColumn(matrix, columnIndex);
System.out.println();
System.out.println("The " + columnIndex + " column has a sum of " +reType);

}

public static double sumColumn(double[][] matrix, int columnIndex) {

//Assign values to the matrix
System.out.println("The Elements in the matrix:");
for (int row = 0; row < matrix.length; row++) { //start from the 0rth row, don't stop loop until all the rows are done, add 1 to row value each time to satisfy the loop.
for (int column = 0; column < matrix[row].length; column++) { //start from the 0rth column, ... [same]
matrix[row][column] = (int) (Math.random() * 100);           //So for the starting from cell of row 0 column 0 all the way to the max row/column cell, fill up the matrix cells with random numbers
}
}

//Print values in matrix
for (int row = 0; row < matrix.length; row++) {
for (int column = 0; column < matrix[row].length; column++) {
System.out.print(matrix[row][column] + " ");
}
System.out.println();
}
System.out.println();
//Calculate the sum of each matrix column
//notice that first the column is selected, then the rows. This allows the rows to go through the adding function first, thus "summing elements by column".

int total =0; //you have to initialize the variable total in order to use it.
System.out.println("The sum of each column:");
for (int column = 0; column < matrix.length; column++) {
for (int row = 0; row < matrix.length; row++)
total += matrix[row][column]; //Notice that braces {} are not used, but the statement above in continued to below and ends at the semi-colon ;
System.out.print("Sum for column " + column + " is " + total);
System.out.println();
} 